Wire covering for high frequency circuits



June 14, 1938. R. G. ZENDER 2,

WIRE COVERING FOR HIGH FREQUENCY CIRCUITS Filed Oct. 50. 1935 fm enZ OP fi cg/n 207262 6. ZcWZcZ GP Patented June 14, 1933 Raymond G. lender, Chicago; llli, assign Lens Electric Manufacturing 00., Chicago, Ill., a corporation of Illinois Application October 30, 1935, Serial No. 47,445

Claims.

. This invention relates to electrical conductors and moreparticularly to improvements in conductors used for carrying high frequency currents such for example as are found in radio fre- 5 quency circuits of radio apparatus.

. In wires carrying these high frequency currents, theJosses which occur may be avoided to a great ex nt by .practical improvements in the insulation applied on the conductor.

It is the purpose of this invention to provide a circuit or hook-up wire for use in all places where thewire is to carry current at the higher frequencies including radio frequencies of the ordinary broadcast band and the higher short wave is frequencies which run up into the millions of cycles. This conductor and its insulationis designed to prevent the losses now present in the well known rubber, cotton, and silk covered wires I have descovered that, by combining a certain textile with a particular impregnating substance, I'obtain a remarkable reduction in certain of the losses at high frequencies, which reduction is entirely unexpected from the known characteristics of the two materials. Much of the loss in textile insulation at the higher frequencies can I be traced to impurities present in fibre, moisture,

saline trotlucedduring the process of manufacturing v dyes for such textile insulation. I find that the' power factor loss and the phase angle for any.

particular conductor can be varied considerably by the type of insulation and impregnating *qompound used on the conductor. It will be shown hereinafter that, by combining the proper textile covering with the'proper impregnating material,

power factor losses may be reduced beyond normal expectation at high frequencies in the short wave band. l r 40 1"or convenience in identifying the various parts of the conduc r and covering, I will describe the invention y reference to the accompanyins drawing wherein the figure is-a plan "view of a conductor covered with a braided cov- 45 ering embodyins the present invention.

In the drawing, the numeral l refers to -a tinned copper conductor which may be either of the solid-or stranded type. Upon this conductor thereis provided a braided covering 2 consisting 9 of three end cellulose acetate textile. Over the layer 2 of braid is a second layer 3 braided in same fashion. This-outer layer may contain,

'wherever' 'needed' for identification purposes, a tracer thread 4 suitably colored for identification.

II Tim strands or tracer thread aroused so that diluents and minerals in ionic form inreadily.

various combinationsof colors may be obtained The threador yarn used is a cellulose acetate substance made from cotton linters.

The cellulose obtained from cotton linters is treated with acetic anhydride in the presence of a catalytic agent usually sulphuric acid to produce a cellulose acetate which is freed of all free acids by washing with water and then dried.

The cellulose acetate is then R dissolved in a solvent containing acetone and made into fine filaments by passing the solution through tiny apertures into an air chamber where the solvent is evaporated. The filaments are twisted into a yarn of any desired size.

The particular size preferred in the present instance, is

denier 3 end yarn.

This yarn is braided upon theconductor in such fashion as to obtain a covering which may be pushed back from an} end of the conductor for making connections. The yarn is braided in two layers at once, the braiding being done in such fashion as to reduce the number of piques lengthwise on the wire.

be pushed back readily.

This makes the braid more compressible lengthwise on the wire so it can The conductor covered in this fashion is next subjected to sham in an impregnating material.

The impregnation is done in such a way as to prevent inclusion of moisture in the covering. Preferably the conductor is dried in a vacuum tank heated to above 212 F. and then the impregnating material, also heated to above 212 F., is let into the tank so as to completely saturate the insulation. The vacuum drying may-be omitted, and the wire merely immersed in the impregnating material which is kept above 212 F. In,

either case, the conductor isleftin the impreghating bath until the insulation on the conductor is completely impregnated with the impregnating material.

This takes usually about two hours. The finished product is then removed and per--v mitted to dry at ordinary atmospheric temperatures.

The cellulose acetate textile is impregnate with a pure mineral wax free of acids so as to be practically neutral to acidity tests. The wax used is a petrolatum type wax which has a very fine crystalline structure as compared to waxes of the parailin type. This wax also in its prep-'- aration is treated with acetone. The residue afterthe acetone treatment is a pure petrolatum wax melts at 159-15951,

wax of nearly white and translucent appearance.

The color is classified as minus, 12 Saybolt. Th

iii

I have found that this wax in combination with the cellulose acetate textile produces a wire covering which shows remarkable and unexpected reduction in power losses from the wire when used as a conductor for the radio frequency currents.

Heretofore, it has been the practice to use textile coverings for conductors and to impregnate them with a wax, usually beeswax. The textiles commonly used are cotton and silk. I have conducted tests which show that the desirable reduction in power losses with my combination is not the result of one or the other of the materials but to their combination.

In'making up the wire covering, I avoid the use of any materials that tend to break down the resistance of this combination to moisture. Only a small amount of colored textile is used. The inner braid is preferably entirely devoid of any coloring for tracing purposes. In the outer braid where it is necessary to have colors for tracing the conductors, I use no more than 20% of the volume of the outer braid colored. The reason for this is to avoid losses due to metallic ions introduced in the coloring matter during the process of manufacture. The efiect of metallic ions in the coloring can readily be detected at the higher frequencies in the proximity of 12 megacycles.

This combination of cellulose acetate textile with a petrolatum type mineral wax is particularly resistant to breakdown and is not appreciably affected adversely by extreme variations ticularly useful in conductors carrying high frequency current such, for example, as the conductors in the radio frequency stages of radio receiving sets and particularly of short wave receiving sets. In this application where the term radio frequency is used, it is intended to mean those frequencies which are used in broadcasting on both long and short waves. These frequencies are usually considered to range from 50 kc. upward. The change from the usual wire used in such sets to this wire has resulted in gains in output as high as twelve (12) per cent. This gain is remarkable when one considers that only a small portion of the wire used in a receiving set is found in the radio frequency stages.

.A. comparison of the characteristics of this covering with those of the known cotton braid beeswax impregnated coveringand the known purified Tussah silk braid beeswax impregnated improved covering. At 120 F. and90% relative humidity, the, power factor-for the silk covered wire was 19.5%, while that for the wire with my.

- improved covering was .84%. The phase angles for the various coverings, at 70 F. temperature and 50% relative humidity, were as follows:

The insulation resistance at 70 F. and 50% relative humidity was about the same for the silk covering and my improved covering was 100,000 megohms plus. For cotton the insulation resistance was only 195 megohms. At 120 F. and 90% relative humidity, the insulation resistance of the cotton covering dropped to 1.4 megohms while that of the silk dropped to 150 megohms. The insulation resistance of my improved covering dropped only to 11,250 meghoms. This illustrates its superiority in resisting moisture absorption.

From the above disclosure it is believed to be evident that the new combination herein disclosed as a covering for conductors of radio frequency currents is possessed of many advantages over known textile coverings and particularly in reducing power factor losses at the higher frequencies. I do not know the correct scientific explanation for the results obtained. However,

one explanation may be that the textile and the impregnating materials both being subjected to treatment by acetone have similar molecular structures which tend to cut down the energy lost in maintaining the field strength about the conductor. The fine crystalline structure of the impregnating material also permits a more complete impregnation. The wax is able to penetrate into the smaller openings in the textile.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An insulated conductor for carrying radio frequency currents, comprising a wire covered with a cellulose acetate textile, the textile being impregnated with a petrolatum type wax which is substantially devoid of acid and which has a melting point of at least 155 F., said wax having a microcrystalline structure, the insulation resistance of the impregnated textile covering being above 10,000 megohms at 120 F. and 90% relative humidity.

2. An insulated conductor for carrying radio frequency currents, comprising a wire covered with a cellulose acetate textile, the textile being impregnated with a petrolatum type wax which is substantially devoid of acid and which has a melting point of at least 155 F., said wax having a microcrystalline structure, said covering being substantially free of coloring except for tracer threads on the exterior thereof, which threads constitute less than 20% of the total textile volume in the covering.

3. An insulated conductor for carrying radio frequency currents, comprising a wire covered with a cellulose acetate textile, the textile being impregnated with a petrolatum type wax which is substantially devoid of acid and which has a melting point of at least 155 F., said wax having a microcrystalline structure, said textile being applied directly to the surface of said wire in a pair of braids which braids are compressible lengthwise of the wire to expose a length of the wire beyond the covering for connection purposes.

4. An insulated conductor for carrying radio frequency currents, comprising a wire covered with a cellulose acetate textile, the textile being impregnated with a petrolatum type wax which is substantially devoid of acid and which has a.

meltingpoint of at least 155 F., said wax having a. microcrystalline structure, said textile being applied directly to the surface of said wire in a pair of braids which braids are compressible lengthwise of the wire to expose a length of the wire beyond the covering for connection purposes, the outer braid having colored tracer threads melting bolnt 01' at least 155' 1 a, said wax having a microcrystalline structure, said conductor having a power factor loss not exceeding' 1% atfrequencies up-to 12 melacycles in ordinary work in: temperature and humidity. v

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